1. Field of the Invention
The present invention relates to a measurement system for an automatic chemical analyzer.
2. Description of the Related Art
A measurement system is known which is used with an automatic chemical analyzer and which comprises a turntable on which reaction cells are arranged circumferentially and a detector located at a given position relative to the turntable. As the turntable rotates, the detector measures the absorbances of the reaction cells in turn. In this measurement system, as the turntable turns, the reaction cells pass across the front surface of the detector in turn. The output signal from the detector must be sampled just when each reaction cell arrives at the detection position, whereby the absorbance of each cell is measured.
If the timing of the sampling were not accurately adjusted, the absorbance of a portion different from a liquid sample would not be measured. As a result, the measured value would involve error. Therefore, the setting of the sampling timing is quite important. In a known system, a slit, a chopper, a shutter, and other components are mounted at positions corresponding to reaction cells on the turntable to sense the arrival of each reaction cell at the detection position by an optical sensor.
With the above-described method using an optical sensor, if the number of reaction cells placed on the turntable increases, and if the speed of operation becomes higher, then the slit, chopper, shutter, and other components must be accurately aligned to the positions of the reaction cells on the turntable. As the number increases, the size of each reaction cell decreases. This makes it more difficult to make the alignment, which in turn will deteriorate the cost effectiveness.
It is an object of the present invention to provide a measurement system which is used with an automatic chemical analyzer and permits accurate measurement reproducibility and low-cost measurements.
In accordance with the teachings of the present invention, a measurement system is provided for use with an automatic chemical analyzer having a turntable on which reaction cells, each holding a liquid sample aliquot, are arranged circumferentially and a detector placed in a given position relative to the turntable and acting to measure the absorbances of the reaction cells in turn as the turntable rotates. The measurement system comprises an encoder connected with the turntable, a counter for creating an address signal from the output signal from the encoder as the turntable rotates, and a comparator for comparing the address signal with address values previously found when the reaction cells arrived at a detection position. The address signal is obtained as the count value from the counter. The comparator produces a coincidence signal when a match is found. In response to the coincidence signal, the output signal from the detector corresponding to each reaction cell is started to be accepted.
In one embodiment of the present invention, the aforementioned measurement system has a register and a readout circuit. The register holds address values obtained when the reaction cells reach the detection position. The readout circuit sequentially reads address values for each reaction cell to be measured next from the register in response to the coincidence signal described above and sends the address values to the comparator described above.
An address value obtained when each reaction cell reaches the detection position can be determined based on data obtained by sampling the output signal from the detector in synchronism with the encoder output signal over the whole circumference of the turntable while the reaction cells hold no liquid solution or a liquid exhibiting no absorbance in the measured spectral range is put in the cells.
Furthermore, the address value obtained when each reaction cell reaches the detection position can be determined based on data obtained by sampling the output signal from the detector in synchronism with the encoder output signal over the whole circumference of the turntable while aliquots of a liquid exhibiting absorbance in the measured spectral range are put in the cells.
Other objects and features of the present invention will appear in the course of the description thereof, which follows.